1. Field of the Invention
The invention relates to drilling unit apparatus and more particularly to drilling unit apparatus of the type having
a housing; PA0 a drilling spindle housing means axially moveable within said housing; PA0 a drilling spindle rotatably received within said housing and driven by a driving means; PA0 a plunger connected to the drilling spindle housing means and adapted to move axially with the drilling spindle housing means within said housing; PA0 piston means slideably received within said housing and operatively connected to the plunger to move it in upward or downward direction respectively.
2. Description of Related Art
Drilling devices of the aforementioned type are known. One of the purposes, for which they are used, is, within an arrangement of a multiplicity of such drilling units, the boring of holes in printed circuit boards. In this connection it is desirable to reduce the space occupied by one drilling unit as much as possible in order to be able to drill as many holes as possible at the same time, i.e. with one stroke of said multiple drilling units arrangements. Usually, sealing rings or other sealing members provided between the above mentioned parts of the drilling unit require additional space in a plane extending parallel to the printed circuit boards and thereby limit the number of units to be put together and thereby also limit the number of holes, which can be drilled into one board simultaneously.
If the accuracy, with which the drilling tool of such drilling unit can be fed to a particular spot of such printed circuit board, is to be increased, it is necessary to increase the accuracy of the bearing surfaces for the drilling spindle housing means, within said aforementioned housing. This requires an increase of the accuracy of the bearing means, within which the afore said spindle housing and said plunger move. However, when the accuracy of these parts, especially the bearing surfaces extending in axial direction, is increased, it appears that even slight misalignments between the plunger and the drilling spindle housing means, which form a unit and/or between the surfaces, which form bearing means for parts of said unit, lead to clamping, jamming, or blocking of the one of the mentioned components against another one.
A further problem with drilling units of the aforementioned type appears as a consequence of the fact that sealing means mostly are as gaskets. Irregularities of movement of the drilling spindle housing, within said aforementioned housing can occur, since gaskets of elastic material (such as e.g. plastic or rubber) have a tendency to stick to metallic surfaces, which move relative to them. Therefore, the motion of the drilling spindle will be irregular, i.e. interrupted by jerks or the like. Since modern printed circuit boards involve a plurality of layers of different materials, in which it is absolutely essential that accuracy of depth of drilling can be accuractly controlled, it is necessary to avoid such jerks or similar irregularities.